Interest Grabber Getting Through Section 10-1 Interest Grabber Getting Through Materials move through cells by diffusion. Oxygen and food move into cells, while waste products move out of cells. How does the size of a cell affect how efficiently materials get to all parts of a cell? Work with a partner to complete this activity. 1. On a sheet of paper, make a drawing of a cell that has the following dimensions: 5 cm x 5 cm x 5 cm. Your partner should draw another cell about one half the size of your cell on a separate sheet of paper. 2. Compare your drawings. How much longer do you think it would take to get from the cell membrane to the center of the big cell than from the cell membrane to the center of the smaller cell? 3. What is the advantage of cells being small? Go to Section: 1

Section Outline 10–1 Cell Growth A. Limits to Cell Growth 1. DNA “Overload” 2. Exchanging Materials 3. Ratio of Surface Area to Volume 4. Cell Cycle Go to Section: 2

Why can’t cells just get bigger and bigger? Why do cells need to divide? What is the cell cycle? What are the stages of Mitosis? What regulates cell division? What happens if cells just keep on dividing?

What limits Cell Growth? Materials (nutrients, wastes, signals, etc.) have to travel farther to get to and from the cell membrane. DNA demands More proteins must be made from its DNA directions. A large cell would need more information from the command center and the ability to make more proteins, store food, water etc. 4

A. DNA Overload If a cell gets too big, then there isn’t enough DNA directions to make all of the needed proteins. Imagine we were doing a lab to make a particular protein in class and we all had to share a single set of directions.

What are the surface area to volume ratio problems? As a cell gets larger its surface area to volume gets smaller. That means that a larger cell has less surface to get nutrients to the center. 6

Cell size is limited. Volume increases faster than surface area. There aren’t enough places on the membrane to get enough stuff in and out of the cell for the increasing volume that needs materials.

B. Can’t Move Materials Efficiently Imagine 4 students in the corners of the gym passing an egg diagonally across the gym. Would be easier or harder for these 4 students to pass an egg in our classroom? If the cell gets too big, food, gases, etc. cannot travel across the cell fast enough. Volume grows faster than surface area of the cell membrane. surface area – the total area of the cell membrane Volume – how much material is in the cell

What are the problems that cell division solves? Each daughter cell receives its own set of DNA instructions. Each daughter cell is smaller and has a greater surface area, more materials can pass through the cell membrane.

KEY CONCEPT Cells have distinct phases of growth, reproduction, and normal functions.

A. Why do we need more cells? Reproduction - Make more organisms Growth and Development – all organisms start out as a single cell Repair and Replacement – millions of our cells die every second of every day

Checkpoint Does surface area or volume change faster as a cell grows? What are two problems a cell may have if it grew too big? Why do we need to make more cells? ANY QUESTIONS?

Interest Grabber 10-2 Cell Cycle Section 10-2 Interest Grabber 10-2 Cell Cycle The cell cycle represents recurring events that take place in the period of time from the beginning of one cell division to the beginning of the next. In addition to cell division, the cell cycle includes periods when the cell is growing and actively producing materials it needs for the next division. 1. Why is the cell cycle called a cycle? 2. Why do you think that it is important for a cell to grow in size during its cell cycle? 3. What might happen to a cell if all events leading up to cell division took place as they should, but the cell did not divide? Go to Section: 13

What are the contents of the nucleus? Nucleolus: Small dense area in the nucleus where production of ribosomes begins. DNA: Genetic storage chains Chromatin: Condenses into chromosomes 14

What are the chromosomes? They carry the DNA strands and proteins. The number of chromosomes identifies the organism. (Humans have 46) Before cell division chromosomes are replicated. What are chromatids? The chromosome becomes a chromatid at the beginning of cell division. Two daughter chromatids are formed with a centromere at the center. 15

B. Cell Division Requires Preparation! Do we have two of everything in our cells? NO! Most important = Cells only have one set of DNA instructions!! First step in cell division is make a copy of the DNA. Then copies must be separated and sorted into the two sides of the cell. Then cell can split into two.

Cell or Binary FISSION – Prokaryotes Divide Single strand of circular DNA copied DNA separates to opposite sides of the cell Cell membrane/wall divides into two cells

D. Asexual Reproduction Reproduction of genetically identical offspring from a single parent (NO SEX!) Prokaryotic fission produces clones! Daughter cells are identical to parent cell and only one cell needed to make more organisms. One way some organisms reproduce.

Asexual Reproduction: Fission Bacillus undergoing Fission

E. Eukaryotes divide to make identical cells too. More stuff to worry about nucleus with nucleolus and nuclear membrane Chromosomes – not just one all that ‘stuff’ in the cytoplasm has to be dealt with. Nucleus must divide before the cell can.

The cell cycle has four main stages. The cell cycle is a regular pattern of growth, DNA replication, and cell division. During the cell cycle a cell grows; prepares for division; and divides to form two daughter cells, each of which begins the cycle again

2 Phases of the cell cycle with each divided into more phases: Interphase and Mitosis Gap 1 (G1): cell growth and normal functions DNA synthesis (S): copies DNA Gap 2 (G2): extra organelles and other materials needed for division are made

Events of the Cell Cycle 2. M phase = when cell is actually dividing quick phase Broken into 2 more phases Mitosis = division of the nucleus Prophase, metaphase, anaphase & telophase (PMAT) Cytokinesis = division of the cytoplasm

The Cell Cycle Draw this in your notes! G1 M PHASE S G2

Cells divide at different rates. The rate of cell division varies with the need for those types of cells. Some cells are unlikely to divide (G0).

Surface area must allow for adequate exchange of materials. Cell growth is coordinated with division. Cells that must be large have unique shapes.

Checkpoint Why do eukaryotes need more preparation for cell division? What are the two main phases of the cell cycle? What happens during the S phase? What are the two parts of the M phase? ANY QUESTIONS?

Mitosis and Cytokinesis

KEY CONCEPT Cells divide during mitosis and cytokinesis.

Chromosomes condense at the start of mitosis. DNA wraps around proteins (histones) that condense it. DNA double helix DNA and histones Chromatin Supercoiled DNA

WHY? Organizes DNA so easy to separate copies correctly during cell division

Chromosomes made of two identical chromatids. chromatids - duplicated chromosomes attached at the center by the centromere Centromeres - like a “twist tie” that holds the sister chromatids together. # of centromeres = # of chromosomes centromere Draw/label in your notes!

DNA copied in S phase condenses into chromosomes during Prophase.

Interphase prepares the cell to divide. Mitosis and cytokinesis produce two genetically identical daughter cells. Parent cell centrioles spindle fibers centrosome nucleus with DNA Interphase prepares the cell to divide. During interphase, the DNA is duplicated.

Mitosis divides the cell’s nucleus in four phases. During prophase, chromosomes condense and spindle fibers form.

Mitosis divides the cell’s nucleus in four phases. During metaphase, chromosomes line up in the middle of the cell.

Mitosis divides the cell’s nucleus in four phases. During anaphase, sister chromatids separate to opposite sides of the cell.

Mitosis divides the cell’s nucleus in four phases. During telophase, the new nuclei form and chromosomes begin to uncoil.

Cytokinesis differs in animal and plant cells. In animal cells, the membrane pinches closed. In plant cells, a cell plate forms.

Prophase – DNA condenses, nuclear membrane dissolves, spindles form 1. Mitosis Division of the nucleus has 4 steps PMAT Prophase – DNA condenses, nuclear membrane dissolves, spindles form Metaphase – Chromosomes line up on the equator (mid-line) Anaphase – Chromatids pulled apart Telophase – nuclear membrane reforms and cytokinesis begins

Label handout! STAGES OF MITOSIS Spindles pull chromatids apart INTERPHASE G1, S, G2 Normal activities DNA & stuff copied 1. PROPHASE DNA condenses Spindles form at poles Nuclear membrane dissolves Single chromosomes at ends nuclear membrane reforms Cytokinesis 4. TELOPHASE STAGES OF MITOSIS 2. METAPHASE 3.ANAPHASE Label handout! Chromosomes line up on cell “equator” Spindles pull chromatids apart

Prophase Metaphase Anaphase Telophase Stages of Mitosis “first” “middle” Anaphase “apart” Telophase “far” or “separate”

2. Cytokinesis - division of cytoplasm takes place during telophase animal cells – cytoplasm is pinched inward by cell membrane plant cells – a cell plate forms midway

Checkpoint Place these in order and name each stage.